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a: 3/7x4/5=12/35
2/5+3/4=8/20+15/20=23/20
b: 2/5:4=2/20=1/10
1/4+2=9/4
c: 2/5:2/3=3/5
2/3-3/8=16/24-9/24=7/24
a: =84/12+9/12-10/12=83/12
b: =32/5x7/6=224/30=112/15
c: =6/12+8/12+9/12=23/12
d: =16/20+25/20+7/20=48/20=12/5
a) Cách 1 : (3/4 + 1/2) x 5/7
= 5/4 x 5/7
= 25/28
Cách 2 : (3/4 + 1/2) x 5/7
= 3/4 x 5/7 + 1/2 x 5/7
= 15/28 + 5/14
= 25/28
b) Cách 1 : 5/7 x 13/21 + 2/7 x 13/21
= 65/147 + 26/147
= 13/21
Cách 2 : 5/7 x 13/21 + 2/7 x 13/21
= (5/7 + 2/7) x 13/21
= 1 x 13/21
= 13/21
câu c tự làm
\(a,\dfrac{3}{4}-\dfrac{2}{5}+\dfrac{5}{12}=\dfrac{45}{60}-\dfrac{24}{60}+\dfrac{25}{60}=\dfrac{46}{60}=\dfrac{23}{30}\\ b,\dfrac{15}{7}-\dfrac{4}{3}-\dfrac{2}{9}=\dfrac{135}{63}-\dfrac{84}{63}-\dfrac{14}{63}=\dfrac{37}{63}\\ c,\dfrac{3}{5}+\dfrac{2}{5}\times\dfrac{4}{5}=\dfrac{15}{25}+\dfrac{8}{25}=\dfrac{23}{25}\\ d,\dfrac{4}{5}-\left(\dfrac{6}{15}+\dfrac{1}{5}\right)=\dfrac{4}{5}-\dfrac{1}{5}-\dfrac{2}{5}=\dfrac{1}{5}\)
a,Cách 1: (6/11 + 5/11 ) x 3/7 Cách 2 :(6/11 + 5/11) x 3/7
= 1 x 3/7 =6/11 x 3/7 + 5/11 x 3/7
= 3/7 = 18/77 + 15/77
= 3/7
b, Cách 1:3/5 x 7/9 - 3/5 x 2/9 Cách 2 :3/5 x 7/9 - 3/5 x 2/9
= 7/15 - 2/15 = 3/5 x (7/9 - 2/9 )
= 1/3 = 3/5 x 5/9
= 1/3
c, Cách 1:(6/7 - 4/7) : 2/5 Cách 2: ( 6/7- 4/7 ) : 2/5
= 2/7 : 2/5 = 6/7 : 2/5 - 4/7 : 2/5
= 5/7 = 15/7 - 10/7
= 5/7
d,Cách 1:8/15 : 2/11 + 7/15 : 2/11 Cách 2:8/15 : 2/11 +7/15 : 2/11
= 88/30 + 77/30 =(8/15+7/15) :2/11
= 11/2 = 1 : 2/11
= 11/2
Bài 2 cậu tự làm nhé !
a)2/5 + 3/4 = 8/20 + 15/20 = 23/20
e) 1/4+2 = 1/4 + 2/1 = 1/4 + 8/4 = 9/4
b)2/3 - 3/8= 16/24- 9/24= 7/24
g)2/5 nhân 3 = 6/5
c)3/7 nhân 4/5 = 12/35
f)2/5:4= 2/5 x 1/4 = 1/10
d)2/5:2/3 = 2/5 x 3/2 = 6/10= 3/5
5-2/3= 5/1- 2/3 = 13/3
a: 2/3
b: =5/2x22/35=110/70=11/7
2/3
11/7